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It was probably inevitable that people would think of Los Angeles as a desert.

I mean, I get it. You grow up someplace like Massachusetts, where water falls out of the sky once a week and makes rivers a half mile across that never dry up, where there's so much moisture in the air that it's hard to see more than two miles away even if the view wasn't blocked by a wall of green, which it always is.

And then you come out to the California coast, with its brown summer hills and rivers that a housecat could leap without wetting her feet, where you actually have to water your lawn to keep it alive. I grew up in the Great Lakes and came west in my 20s. I understand the temptation to call Los Angeles a desert. I really do.

Gentlemen, today you can walk out that door, turn right, hop on a streetcar and in twenty-five minutes end up smack in the Pacific Ocean. Now you can swim in it, you can fish in it, you can sail in it but you can't drink it, you can't water your lawns with it, you can't irrigate an orange grove with it. Remember we live next door to the ocean but we also live on the edge of the desert. Los Angeles is a desert community. Beneath this building, beneath every street there's a desert. Without water the dust will rise up and cover us as though we'd never existed!

Makes sense. And yet there are two important facts to keep in mind when deciding whether to use this soliloquy from "Chinatown" as a basis for your climatic classification of the Los Angeles basin:

"Chinatown" is a work of fiction.

The person speaking the above lines in that work of fiction, fictional former Los Angeles Mayor Sam Bagby, is speaking to drum up support for a shady dam and aqueduct deal, and it can reasonably be assumed that his speech was written as hyperbole.

Screenwriter Robert Towne intended "Chinatown" as a broad satire of the real-life California Water Wars, and he borrowed the hyperbole faithfully. Though Los Angeles' earliest promoters extolled the young city for the abundance of its water, it became clear well before the end of the 19th century that the basin's braided rivers and native cienegas wouldn't support the kind of grandiose development speculation L.A.'s founding fathers had in mind.

As retired Cal Poly Pomona professor Ralph Shaffer has documented, the predominant PR portrayal of Los Angeles shifted suddenly from "L.A. as Eden" more toward the desert Eden became After the Fall. As Shaffer wrote in a rejected 2003 Op-Ed submitted to the Los Angeles Times (and kindly saved from history's dustbin by Kevin Roderick at LA Observed);

In support of legislation in the 1880s to divert river water for the purpose of irrigation, [Times magnate Harrison Gray] Otis reprinted an article from San Francisco's Alta California that characterized opponents as "in favor of restoring Southern California to its primeval condition of wilderness and desert," abandoning it to "the lizard, horned toad and burning sun." No doubt a bit of Bay Area snobbery was involved in the Alta's description, but Otis knew a winning argument when he read one. He resurrected it two decades later to coax voters into supporting the Owens Valley aqueduct bonds.

Over the years the "Los Angeles is a desert" theme has appeared regularly in The Times. Columnists, reporters, editors, politicians and op-ed writers all pushed the idea. A quarter century ago Remi Nadeau, quoted in the recent editorial, wrote in an op-ed piece that "Los Angeles is by far the largest city ever built in a desert."

Some proponents of the Los Angeles as desert meme pulled out all the stops in their rhetoric. Witness this effusive 1886 letter to the editor of the Los Angeles Times via Shaffer's site, a response to the state Supreme Court's decision in Lux v. Haggin that California water rights followed English Common Law, thus granting priority in water rights to landowners along the riverbanks:

Is there any bar at all between our beautiful homes, our orange groves and vineyards, and ruin and destruction, save our own strong right arms and faithful Winchesters? Why may not Pasadena again be relegated to her primeval condition as a first-class pasture ranch for the festive jack rabbit and the baa-ing sheep? What is to prevent Los Angeles from once more becoming the favorite breeding place of the frisky squirrel, and the plaintive ground-owl? ... "It's English, you know," this decision, and we ought not to complain. What shall prevent the impoverished descendants of some of the old Conquistadores from returning the waters of the Santa Ana to their original bed, wherewith to quench the thirst of a few miserable bovines and broncos, and burros. Riverside and Anaheim, and Orange and Santa Ana, would perish from the face of the earth, but it would be in accordance with law -- as at present defined by a majority of our Supreme Court. Dust and desert they were a few short years since, and to dust and desert they may return.

Despite the booster propaganda as it echoes down through the ages, Los Angeles is no desert. It is not even, as some more cautious observers would have it, "semi-arid." At least not under the most commonly used system of climate classification, the Köppen system, in use in one form or another since before the above letter-writer predicted a jackrabbit Reconquista on Colorado Boulevard. Under the Köppen system, Los Angeles and its surround are classified as possessing a Mediterranean climate, along with much of the rest of Coastal California and much of the Pacific Northwest.

Some of the confusion is due to the shifting definition of the word "desert." There was a time, two hundred years ago, when people used the word to mean any land that had no forest cover. Much of Nebraska qualified as desert under this definition, and in fact the High Plains were referred to as the Great American Desert through much of the 19th Century, despite the presence of lush waist-high prairie grasses in thick sods running for hundreds of miles in all directions.

One common definition of "desert" centers on potential evapotranspiration: if the amount of moisture that could potentially evaporate exceeds the amount of precipitation, then the region is a desert under that definition. Under this definition, some parts of the L.A. basin could be considered deserts in exceptionally hot dry years. And so could parts of Madagascar that get 24 inches of rain a year, more than Oakland generally gets.

These days, many biogeographers hew to the definition of desert advanced by scientist Peveril Meigs, in which a place is considered a desert if it receives less than 10 inches of precipitation a year. It's not a perfect definition of a desert; Meigs' definition would exclude Tucson, for instance, a canonical desert city if ever there was one.

The more we learn about deserts, the more we realize that there may never be a simple metric to that allows us to draw a precise boundary between desert and non-desert. What we do know is that deserts are characterized by extremes rather than averages; that there's something in the environment -- periods of drought, high temperatures, saline soils, or a combination of several such factors -- that make living there difficult. A piece of the Mojave desert may average 12 inches of rain a year, but that average may consist of one year with 36 inches and several on either side with no precipitation at all. Temperatures may average in the 60s but peak at 127 and bottom out at 20 below. The desert is a place where native organisms either survive extremes, or they don't survive at all.

There are extremes to be had in Los Angeles, but they mainly involve either wealth or competitive sports. One day in September 2010 the temperature in Los Angeles maxed out at 113, and it was news across the country. A hundred miles east, we've had temperatures above that for the last few days, but CNN is strangely absent from the scene. When non-cultural extremes take place in Los Angeles, people notice and talk about them for years... which pretty much excludes L.A. from consideration as a desert by definition.

Where the natural vegetation of Los Angeles remains, it survives predictable cycles. The chaparral plants have adapted ways to survive periodic fires, and now and then they have to put those skills to use. But the toyons in the hills predictably survive the predictable dry seasons, the bunchgrasses set seed in anticipation of wet autumns that almost always come, and marine layer fogs reliably cool the city in June when actual deserts start to climb above triple-digit temperatures.

Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments weekly about desert issues on KCET. Read his recent posts here.

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